P0128
DTC P0128 ENGINE COOLANT THERMOSTAT OPEN STUCK
Component Location:
GENERAL DESCRIPTION
An Engine Coolant Temperature Sensor (ECTS) monitors the temperature of the coolant. This input is used by the PCM for engine control and as an enabling criteria for same diagnostics.The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria may not run when expected.
DTC DESCRIPTION
If the engine coolant temperature does not reach warm state when model coolant temperature has been reached a thermostat regulating temperature, the PCM judged this as a fault and DTC is set.
NOTE: If any codes relating to ECTS, IATS circuits are present, do all repairs associated with those codes before proceeding with this troubleshooting procedure.
Specification:
Schematic Diagram:
SIGNAL WAVEFORM & DATA
This figure shows the wave form at terminal 4 of ECTS at idle rpm.
1. In case the voltage of ECTS is always 4 V.
Possible cause : Open ground circuit Open inner circuit of component
2. In case, when engine is cold,the voltage is below 0.5 V.
Possible cause: Short between PCM and sensor Faulty PCM
When checking the wave form,watch carefully if there is any sudden change in signal.
The ECTS and IATS signals should be smooth and continuous without any sudden changes. When the engine is cold, the ECTS and IATS signals should look similar, depending on the ambient air temperature. After warm-up, the IATS signal should not changes significantly, while the ECTS signal should drop. This indicates that the normal increase of the engine coolant temperature is larger than the normal increase of the intake air temperature as the engine warms up.
MONITOR DTC STATUS
This is the inspection procedure to determine whether it is present DTC or memoried one by monitoring the current signal or by using the function of oscilloscope with Hi-scan pro
1. Connect scantool to Data Link Connector(DLC).
2. Warm up the engine to normal operating temperature.
3. Monitor the "ECTS signal" parameter on the scantool.
NOTE: If the output data changes as temperature changes, the sensor is good
If the ECTS output is in inverse proportion to water temperature, the sensor is normal.
Service standard
When ECT is 0 °C(32 °F): 4.27 ± 0.3 V
When ECT is 20 °C(68 °F): 3.44 ± 0.3 V
When ECT is 40 °C(104 °F): 2.72 ± 0.3 V
When ECT is 80 °C(176 °F): 1.25 ± 0.3 V
4. Is parameter displayed within specifications?
YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared.
Thoroughly check connectors for looseness, poor connection, bending, corrosion,contamination,deterioration, or damage Repair or replace as necessary and then go to "Verification of Vehicle Repair" procedure.
NO: Go to "W/Harness Inspection" procedure
TERMINAL & CONNECTOR INSPECTION
1. Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical Systems, and mechanical or chemical damage.
2. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination,deterioration, or damage.
3. Has a problem been found?
YES: Repair as necessary and go to "Verification vehicle Repair" procedure.
NO: Go to "Component Inspection" procedure.
COMPONENT INSPECTION
The resistence check of ECTS component is for finding whether open circuit is in the component.
1. Cooling System inspection
1. Check cooling system coolant level and fill if low.
2. Check for a proper cooling system operation. Especially check that cooling and condenser fan working normally.
3. Remove the thermostat and check the following items:
1. Stuck or damaged Full open lift: 8.5 mm(0.33 in) or more
2. Verify the temperature at which the valve begins to open.Initial valve opening temperature: 82 °C(179.6 °F)
Full valve opening temperature: 95 °C(203 °F)
4. Is a problem found?
YES: Repair as necessary and go to Verification vehicle Repair" procedure
NO: Go to "Check ECTS" as below.
2. Check ECTS
1. Measure resistance between terminal 1 and 2 of sensor connector(To sensor side)
Specification
20 °C(68 °F) : 2.27-2.73 kOhms
80 °C(176 °F): 0.29-0.32 kOhms
2. Does each resistance indicate continuity circuit?
YES: Go to "Check PCM" as below.
NO:
- Open circuit ECTS.
- Repair as necessary and then go to "Verification of Vehicle Repair" procedure
3. Check PCM
The purpose of checking ECM is to determine whether there is any malfunction of PCM
1. Ignition "OFF"
2. Connect Scantool and Engine "ON"
3. Select simulation function on scantool.
4. Simulate voltage at terminal 1 of ECT sensor signal connector.
5. Verify ECTS voltage to change while raising or lowering simulation voltage with scan tool within 0.5 - 3.5 V
Specification : If the data is changeable as simulation voltage changes, it's OK
6. Is ECT sensor signal value changed according to simulation voltage?
YES: Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage Repair or replace as necessary and then go to "Verification of Vehicle Repair" procedure.
NO: Substitute with a known-good PCM and check for proper operation. If the problem is corrected, replace PCM and then go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verify that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code (DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs.
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions.
4. Monitor that all rediness test have been verified as "Complete"
5. Are any DTCs present?
YES:Go to the applicable troubleshooting procedure.
NO: System is performing to specification at this time.